It is Lawrence Medical Systems' hypothesis that the noninvasive determination of cardiac output will identify the pathophysiologic basis of a patient's hypertension. That is, whether the hypertension is due to elevated cardiac output, increased systemic vascular resistance, or both. Knowing this will be useful in selecting the best anti-hypertensive regimen for that patient, resulting in better blood pressure control, fewer medications, fewer adverse side effects, and better prescription compliance. If this hypothesis can be proven, Lawrence will be in an excellent position to gain the major market share of a $492 million potential market in the cardiologist and internist's office. In order to develop this market potential, innovation is required in two areas. 1) The ease of use of noninvasive cardiac output measurement must be enhanced to match the expected operators skill level found in the outpatient treatment setting. 2) Hypertension treatment practice must be changed from the accepted Stepped Care drug therapy protocols to one that selects the best drug treatment regimen based on each patient's hemodynamic pattern. In Phase I, Lawrence's current continuous cardiac output measurement system will be modified and its accuracy will be verified for use in the physician's office. Phase II will be a multi-center study of the benefits of hemodynamic controlled drug therapy for hypertension.